The present invention relates to a method for preparing intrinsically conductive copolymers (ICPs) from polymerizing at least one cyclic heteroatom-containing monomer such as aniline, thiophene, pyrrole, furan, and the derivatives or substituted forms of the respective monomers and an emulsion latex which remains substantially stable in the presence of the cyclic heteroatom-containing monomers and during the course of the polymerization. This invention further relates to the compositions of the intrinsically conductive copolymers prepared in accordance with the method. In addition, the invention also relates to a method of preparing blends of ICPs with carbonaceous materials, metal oxide powders and polar polymers.
ICPs are known to be useful for a number of applications. For instance, ICPs maybe used as part of a coating formulation for inhibiting corrosions of metals, particularly iron or iron based metals such as carbon steel and different types of stainless steel, aluminum, aluminum alloys, nickel and others.
It is known that a number of cyclic heteroatom (O, S, and N)-containing monomers such as aniline, furan, pyrrole, thiophene and their derivatives can be polymerized to yield ICPs. Most of such polymer products are known to be intractable. Typical ICPs do not have very high solubilities in commonly used solvents, and they are usually thermally unstable, infusible and brittle. As a result, most ICPs cannot be processed easily by conventional methods used for processing other polymers. Attempts to solve the processing problems over the past several years produced only limited success. As a result, many predictions that these conductive polymers would usher in novel products such as polymer batteries, electrical wires, or capacitors have largely not been realized.
Polyaniline is an example. It is commonly prepared by an oxidative polymerization of aniline in the presence of a protonic acid. The polymer product is an insoluble green solid precipitate, mostly amorphous and generally insoluble in common organic solvents (see Annis et al., Synthetic Metals, 22:191, 1986). U.S. Pat. No. 5,232,631 describes a number of polyaniline salts prepared by reacting polyaniline in the presence of an acid such as dodecylbenzene sulfonic acid, 1,5-naphthalenedisulfonic acid and p-toluene sulfonic acid. These polyaniline salts are only sparingly soluble in nonpolar solvents. U.S. Pat. No.5,232,631 and U.S. Pat. No. 5,324,453 describe the synthesis of polyaniline from a mixture which consists of an aniline monomer, a protonic acid, an oxidant, a polar liquid such as water and a nonpolar or weakly polar liquid chosen from chloroform, xylene, toluene, decahydronaphthalene and 1,2,4-trichlorobenzene. In such a process, post-polymerization removal of residual organic solvents in the polymer products to an acceptable level may pose a substantial challenge to a prospective manufacturer.
The present invention relates to a (co)polymerization method which overcomes many of the difficulties encountered in the prior art and/or provides improvements to the chemical, physical, or mechanical properties of the resultant ICPs which are prepared from at least one cyclic heteroatom-containing monomer.
The present invention also relates to a method for preparing an intrinsically conductive copolymer comprising: preparing an emulsion latex in a medium; forming a mixture by adding at least one cyclic heteroatom-containing monomer to the emulsion latex in the medium under first condition effective to maintain the emulsion latex in a first stabilized emulsion state; causing the monomer(s) in the mixture to polymerize under a second condition effective to produce the conductive copolymer in a second stabilized emulsion state; and optionally, recovering the intrinsically conductive copolymer.
The present invention further relates to a method, wherein the cyclic heteroatom-containing monomer is selected from the group consisting of aniline, substituted anilines, thiophene, substituted thiophenes, furan, substituted furans, pyrrole, substituted pyrroles, and mixtures thereof.
Another embodiment of the present invention relates to an intrinsically conductive copolymer composition prepared by the invented method. The present invention further relates to different methods of using the ICPs in coating formulations with an option of providing a top-coating over the layer containing the ICPs. More specifically, the present invention relates to a method of using the intrinsically conductive copolymer prepared according to claim 1 or 9, the method comprises preparing a coating composition which comprises the intrinsically conductive copolymer; and applying the coating composition on a surface of a metal to form a first layer, optionally applying a top coat layer over the first layer.
It has been discovered unexpectedly that ICPs can be prepared chemically, electrolytically or electrochemically by emulsion polymerization and/or copolymerization and/or graft copolymerization of at least one cyclic heteroatom-containing monomer in the presence of a stable latex emulsion under conditions effective to maintain such stabilized emulsion conditions in one, two- or multi-stages. Examples of a suitable heteroatom include O, N, and S. More than one heteroatoms may be present in the same cyclic heteroatom-containing monomer or in the ICP itself from different monomers incorporated into the ICP. For the present invention, the resultant ICP product should have an intrinsic conductivity equal to or greater than 5xc3x9710xe2x88x924 Siemens per centimeter, preferably greater than 5xc3x9710xe2x88x922 Siemens per centimeter, more preferably greater than 1 Siemens per centimeter. It is also within the scope of the present invention that the conductivity is increased by doping with a suitable dopant.
Cyclic heteroatom-containing monomers suitable for use to be (co)polymerized in the present invention include, but are not necessarily limited to aniline, thiophene, pyrrole, furan, substituted anilines, substituted thiophenes, substituted pyrroles, substituted furans, and mixtures thereof. They are of the following generalized structures. 
wherein q, r, s, t, w, x, y, and z are independently selected from positive integers and 0(zero); y+z=5; q+r=4; s+t=4; and w+x=4; R1 and R5, are independently selected from the group consisting of H and C1 to C18 linear or branched alkyl groups, H and CH3 are preferred; R2, R3, R4, and R6 are independently selected from H, C1 to C18 linear or branched alkyl groups, aryl groups such as phenyl or substituted phenyls, a benzo group (occupying two adjacent sites on the ring), C(xe2x95x90O)OH, C(xe2x95x90O)H, CH2OH, CH2OC(xe2x95x90O)R7 where R7 is selected from C1 to C6 linear or branched alkyl groups, CH2CH2OH, CH2SH, CN, CH2NH2, C(xe2x95x90O)NH2, CH2CN, Oxe2x80x94R8 where R8 is selected from C1 to C6 linear or branched alkyl groups, C(xe2x95x90O)R9 where R9 is selected from C1 to C6 linear alkyl groups, and mixtures thereof. To the extent that it discloses such polymerizable heteroatom-containing cyclic monomers, U.S. Pat. No.5,648,416 is incorporated herein by reference. Many of these compounds can be purchased from Aldrich Chemical Company, ICN Biomedicals, Inc., and other chemical suppliers.
Examples of substituted monomers include, but are not necessarily limited to, alkyl or aryl substituted monomers such as 2-methylaniline, 2-ethylaniline, 3-ethylaniline, 2-methylthiophene, 3-methylthiophene, 3-hexylthiophene, benzo[b]thiophene, 2-methylpyrrole, 2-methylfuran, and mixtures thereof. Many of these cyclic heteroatom-containing monomers may be considered as xe2x80x9caromaticxe2x80x9d in nature. In general, these cyclic monomers are characterized by being insoluble or substantially insoluble in, or immiscible or substantially immiscible with water (less than about 1 g per 100 g of water).
An aqueous emulsion latex is a preferred emulsion latex for the present invention. Examples of such an emulsion latex, also referred to as a binder in many references, which may be used in a stabilized or substantially stabilized emulsion state, include, but are not necessarily limited to homopolymers or copolymers prepared from one or more monomers selected from one or more of the following groups:
Group A:
ethylenically unsaturated carboxylic acids and their esters such as acrylic acid (AA), methacrylic acid (MAA), methyl acrylate (MA), ethyl acrylate (EA), propyl acrylate (PA), butyl acrylate (BA), 2-ethylhexyl acrylate (2EHA), methyl methacrylate (MMA), ethyl methacrylate, propyl methacrylate, butyl methacrylate (BMA), poly (ethylene glycol[200/400] monomethacrylate and mixtures thereof;
Group B:
vinyl compounds such as ethylene, propylene, butadiene (BD), substituted butadienes such as alkylbutadienes-isoprene, allyl acrylate, allyl methacrylate(ALMA), vinyl chloride (VCM), vinyl acetate (VAM), styrene (ST), p-methylstyrene (PMS), 4-vinylpyridine (4 VP), 2-vinylpyridine (2 VP), N-vinylpyrrolidone (NVP), styrene sulfonic acid(SSA) and mixtures thereof;
Group C:
unsaturated amides such as acrylamide, methacrylamide, N-methylolacrylamide and mixtures thereof;
Group D:
other unsaturated monomers containing nitrogen or silicon such as dimethylaminoethyl acrylate, trimethylvinylsilane and mixtures thereof;
It is understood that the mixtures mentioned above and elsewhere must be chemically and physically compatible with one another as well as other ingredients under the reaction conditions.
The total amount(s) of a monomer or monomer mixtures selected from Groups A and/or B should be in the range of from 85% to 100%, preferably from 97.5% to 100% by weight of the resultant polymer, based on the total weight of the polymer in the emulsion latex.
The amount(s) of a monomer or monomer mixtures selected from Groups C and/or D, if there are any, should be in the range of from 0% to 50%, preferably from 0% to 5%, most preferably from 0% to 2.5%, by weight in the polymer, based on the total weight of the polymer in the emulsion latex.
Examples of preferred polymers (binders) for the emulsion latex suitable for the present invention include, but are not necessarily limited to: poly(MMA-BA=15-85), poly(MMA-4VP=85-15), poly(MMA-MAA=80-20), poly(BA-BD=60-40), poly(MMA-EA-4VP=70-15-15), poly(MMA-EA-4VP=65-20-15), poly(MMA-EA-4VP=45-40-15), poly(MMA-EA-4VP=70-15-15), poly(ST-4VP=85-15), poly(MMA-EA-SSA=50-45-5), poly(MMA-EA-ALMA=95.8-4-0.2), poly(BA-ST-ALMA=80-18-2) and mixtures thereof.
The solids content of a suitable aqueous emulsion latex for the present invention is in the range of from 5% to 90%, by weight, based on the total weight of the aqueous emulsion latex, preferably in the range of from 10% to 75% by weight, more preferably in the range of from 20% to 50% by weight. Many emulsion seed particles used in the examples described herein are derived from a 30% solids content aqueous emulsion latex.
An emulsion latex having a desired composition as described herein may be prepared form polymerizing the selected monomers by a number of methods or processes disclosed in the prior art such as xe2x80x9cEmulsion Polymerization of Acrylic Monomers: May, 1966xe2x80x9d published by the Rohm and Haas Company, Philadelphia, Pa., and xe2x80x9cPolymer Syntheses,xe2x80x9d Vol. I, Chapter 10 by S. R. Sandler and W. Karo, Academic Press, New York, N.Y. (1974). To the extent of relevant descriptions or disclosures of such methods or processes, both references are incorporated herein by reference.
A number of methods or processes are within the scope of the present invention for preparing the ICPs. A method or a process is suitable for the present invention only if the aqueous emulsion latex can be maintained or substantially maintained in a stabilized or substantially stabilized emulsion state during the process when the cyclic heteroatom-containing monomer(s) is polymerized, copolymerized and/or graft copolymerized, particularly in the presence of highly charged cationic species and/or a pH in the acidic range. Any significant or substantial phase separation, collapse and/or agglomeration of the dispersed/suspended emulsion latex micelles or particles would render the method or process not suitable for preparing the desired ICPs of the present invention. Accordingly, the term xe2x80x9csubstantially stabilized emulsion statexe2x80x9d used herein means that there is no significant loss of the original emulsion state during and after the formation of the initial mixture, and during and preferably after the desired polymerization/co-polymerization/graft polymerization reaction has taken place via a single, two- or multi-stage process.
More specifically, one aspect of the present invention involves a method for preparing an intrinsically conductive copolymer composition comprising: preparing an emulsion latex in a medium; forming a mixture which comprises at least one cyclic heteroatom-containing monomer, the emulsion latex in the medium and an additive under a first condition effective to maintain the emulsion latex in a first stabilized emulsion state; and causing the cyclic heteroatom-containing monomer in the mixture to polymerize under a second condition effective to produce the intrinsically conductive copolymer in a second stabilized emulsion state.
Another aspect of the present invention relates to a method for preparing an intrinsically conductive copolymer composition comprising: preparing an emulsion latex in an aqueous medium; forming a mixture which comprises at least one cyclic heteroatom-containing monomer, the emulsion latex in the aqueous medium and an additive under first condition effective to maintain the emulsion latex in a first stabilized emulsion state; causing less than 10% by weight of the cyclic heteroatom-containing monomer based on total weight of the cyclic heteroatom containing monomer in the mixture to polymerize at a first reaction temperature and under second condition effective to produce a precursor to the intrinsically conductive copolymer in a second stabilized emulsion state; and converting the precursor and remainder of the cyclic heteroatom-containing monomer in the mixture at a second reaction temperature and under third condition effective to produce the conductive copolymer in a third stabilized emulsion state, wherein the second temperature is lower than the first temperature.
The cyclic heteroatom-containing polymerizable monomers, many of them considered to be aromatic in nature, are generally insoluble in an aqueous medium, but can be emulsified under proper conditions. In the presence of an emulsion latex, they can be homopolymerized, copolymerized or graft copolymerized by a number of methods including, but not necessarily limited to cationic oxidation polymerization in an acidic aqueous medium, electrochemical anodic deposition and combinations thereof. A method of cationic oxidation polymerization in an acidic aqueous medium (pH value lower than 7.0) is preferred for the present invention.
One embodiment of the present invention relates to a method of using the intrinsically conductive copolymer prepared according to the disclosed methods herein, the method comprises forming a coating composition which comprises the intrinsically conductive copolymer; mixing the coating composition with a top-coating composition to form a blend; and applying the blend on a surface of a metal.
In yet another embodiment of the present invention, a heteroatom-containing polymerizable cyclic monomer or monomer mixture is mixed with an emulsion latex described herein to form a mixture under conditions which are effective in maintaining or substantially maintaining a stabilized or substantially stabilized emulsion state when forming such a mixture and during subsequent polymerization, copolymerization and/or graft copolymerization. The amount of a monomer or monomer mixture used depends on a number of factors, including, but not necessarily limited to: the desired ICP composition, the composition of the emulsion latex, the composition of the monomer or monomer mixture, the complexing agent used, the emulsifying agent used, and other reaction conditions such as pH, temperature, etc.
One way of maintaining a stabilized emulsion state is to have a complexing agent and a non-aromatic emulsifying agent in the aqueous emulsion latex. It is preferred to add such a complexing agent or emulsifying agent prior to or during the time when the monomer is mixed with the emulsion latex to form the mixture.
Without limiting the scope or the spirit of the present invention, it is believed that a complexing agent like xcex2-MCD, as described below, provides a function of transporting a water-insoluble aromatic monomer(s) through the aqueous phase to the surface of the emulsion seed particles. Example of a suitable complexing agent include, but are not necessarily limited to a cyclodextrin, a partially alkylated cyclodextrin, a saccharide, a cycloinulohexose, a cycloinuloheptose, a cycloinuloctose; a calyxarene; a cavitands and mixtures thereof. Preferably, a complexing agent should have or could form a hydrophobic cavity with a hydrophilic exterior surface. More preferably, the hydrophobic cavity is large enough to form a host-guest relationship with the specific polymerizable heteroatom-containing monomer(s) used to prepare the desired ICPs. Descriptions of such a host-guest relationship and the relevant chemistry can be found in many papers published by Professor Donald J. Cram of University of California at Los Angeles, USA.
Examples of cyclic oligosaccharides having a hydrophobic cavity, such as cycloinulohexose, cycloinuloheptose, useful in the method of the invention are described by Takai et al., Journal of Organic Chemistry, 1994, volume 59, number 11, pages 2967-2975. Examples of calyxarenes are described in U.S. Pat. No. 4,699,966, International Patent Publication WO 89/08092 and Japanese patent publications 1988/197544 and 1989/007837. Examples of cavitands are described in Italian patent application 22522 A/89 and Moran et al., Journal of the American Chemical Society, volume 184, 1982, pages 5826-5828.
Preferably, a complexing agent suitable for the present invention is characterized by a solubility of greater than 0.5 g/100 g water, preferably greater than 1.0 g/100 g water, more preferably greater than 2.5 g/100 g water. It is preferred that the complexing agent has the ability to form at least a semi-stable complex, such as a guest-host relationship, with the monomer(s) used. Examples of complexing agents include, but are not necessarily limited to cyclodextrins such as alpha-cyclodextrin (hydrate, xcex1-CD); beta-cyclodextrin (hydrate, xcex2-CD); gamma-cyclodextrin (xcex3-CD); partially alkylated cyclodextrins or cyclodextrin derivatives such as methyl beta-cyclodextrin (xcex2-MCD), sulfated beta-cyclodextrin, triacetyl-beta-cyclodextrin, hydroxypropyl and hydroxyethyl derivatives of alpha, beta, or gamma cyclodextrins; and mixtures thereof. Examples of a saccharide are mon-, di-, tri-, or tetra-saccharides and mixtures thereof. A more preferred complexing agent consists essentially of xcex2-MCD. The amount of a complexing agent used in the mixture is in the range of from 0 to 10 weight percent (wt %), based on the total weight of the monomer(s) used. More preferably, the amount is in the range of from 2 to 5 wt %.
Examples of an emulsifying agent include, but are not necessarily limited to a non-aromatic sulfonate and mixtures thereof. Examples of a non-aromatic sulfonate include SOLUSOL(copyright). Other common commercially available emulsifying agents are sodium lauryl sulfate, TRITON X-100 and TRITON X-200. SOLUSOL is a registered trademark of American Cyanamid Company. TRITON is a registered trademark owned by Union Carbide Corporation.
In addition to a complexing agent and an emulsifying agent, it is preferred to add an additional chemical or additives which tends to further improve the stability of the emulsion state before, during, and after polymerization, copolymerization, and/or graft copolymerization. Examples of such a chemical include, but are not necessarily limited to poly(vinyl acetate), poly(vinyl alcohol), partially hydrolyzed poly(vinyl acetate) which contains vinyl alcohol units, other OH group containing polymers prepared from monomers such as 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 3-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, and mixtures thereof. A preferred additive is an 88/12(by mole) poly (vinyl alcohol)/(vinyl acetate) copolymer.
Continuous and sufficient agitation is one method to maintain or substantially maintain the mixture in a stabilized or substantially stabilized emulsion state before and during polymerization reaction. Alternately, a suitable mixture comprising a suitable monomer(s), a complexing agent and an emulsifying agent may be added continuously to the reactor to effect the desired polymerization reaction.
A mixture which comprises an emulsion latex, a heteroatom-containing polymerizable monomer or monomer mixture, an emulsifying agent and a complexing agent may be formed before conducting the desired polymerization. In a continuous or semi-continuous process or method, the emulsifying agent and/or the complexing agent may be added to the emulsion latex first, or one or both of them can be mixed with the monomer first followed by adding this to the emulsion latex.
Formation of the mixture may be carried out under conditions which allow maintaining or substantially maintaining a stabilized or substantially stabilized emulsion state of the emulsion latex used. The temperature is in the range of from 0xc2x0 C. to 85xc2x0 C., preferably from 4xc2x0 C. to 55xc2x0 C., most preferably from 6xc2x0 C. to 40xc2x0 C. Pressure is generally not very critical unless it is necessary to maintain a more desired concentration of the monomer(s) for the polymerization step. A suitable pressure is in the range of from 10 kPa to 2 MPa. A preferred pressure is in the range of from 50 kPa to 500 kPa. An inert atmosphere also may be used and is preferred. The selection of a particular gas may depend on the reactants used to ensure chemical compatibility. Suitable inert or non-reactive gases include, but are not necessarily limited to nitrogen, argon, carbon dioxide, methane and mixtures thereof. In most cases, nitrogen is a preferred inert gas. Air or diluted air also may be used provided there is no interference with the stability of the components used or the desired polymerization reaction.
In order to effect the desired polymerization, copolymerization, and/or graft copolymerization, either a proper initiator is needed, or an electric current must be applied to the reaction mixture. It is preferred to use a chemical initiator. A preferred initiator comprises a redox pair- a reducible metal compound and an oxidant. Many such initiators or redox pairs are known. Examples of a reducible metal compound include, but are not necessarily limited to Fe(III), Co(III), Cu(II) compounds and mixtures thereof. One such compound is FeCl3. Examples of oxidants include, but are not necessarily limited to ammonium persulfate [APS (NH4)2S2O8], t-butyl hydroperoxide, H2O2, alkyl peroxy bicarbonates such as n-propyl peroxy bicarbonate, peracetic acid, trifluoro peracetic acid, perbenzoic acid and mixtures thereof. A preferred redox pair consists essentially of FeCl3 and (NH4)2S2O8.
When a chemical initiator is used, particularly in an aqueous medium, it is preferred to have a pH value in the acidic region, i.e. lower than 7. It is more preferred to have a pH lower than 4. It is most preferred to have a pH lower than 2 when iron (III) compound or compounds are used as part of an initiator or a redox pair.
The amount of a chemical initiator needed is in the range of from 0.001 wt % to 15 wt %, based on the total weight of the monomer(s) to be polymerized. When a redox pair is used as the chemical initiator, the molar ratio of the reducible metal compound to the oxidant is in the range of from 1:1 to 1:1000, preferably in the range of from 1:10 to 1:100, assuming that the oxidation states or oxidation state equivalents for both change by a ratio of 1. If the ratio is not 1, then the molar ratio has to be adjusted accordingly. For instance, if the reducible metal changes its oxidation state by 2 and the oxidant changes only by 1, the relative molar amount of the oxidant has to be increased by a factor of 2.
The polymerization reaction, (homopolymerization, copolymerization, and graft copolymerization all considered to be within the scope of this invention) of a suitable monomer may be carried out under a number of effective conditions. Such conditions must maintain or substantially maintain a stabilized or substantially stabilized emulsion state of the emulsion latex used. The temperature is in the range of from about 0xc2x0 C. to about 70xc2x0 C. and preferably from 5xc2x0 C. to 55xc2x0 C.
It is preferred that the polymerization reaction is carried out in two stages at two different temperatures. It is more preferred that the temperature of the second stage is lower than the temperature of the first stage. In the first stage, a minimum of 10 weight percent, but not more than 50 weight percent, based on the total weight of the monomer(s) used, is polymerized to produce a precursor to the desired ICP. At the end of this stage, the product should still be maintained in a stabilized or substantially stabilized emulsion state. Not all the monomer(s) need be added at the beginning of the first stage. For instance, an amount of the monomer(s) equivalent to the amount of the precursor desired may be added for the first stage and the remainder of the monomer(s) is added prior to or during the second stage reaction. An example of such a precursor is the preparation of leucoemeraldine when aniline is the selected as the cyclic heteroatom-containing monomer.
The reaction temperature for the second stage is changed, preferably lowered. During this second stage, the remainder of the monomer(s) is further polymerized to produce the desired ICP products. For the present invention, it is not necessary to completely polymerize all the monomers present.
If the reaction is conducted in a continuous reaction system, stage one and stage 2 may represent different reaction zones of a reactor or different reactors. The reaction times for different stages, if there are any, are adjusted to produce the desired ICP. The reaction times may vary for the same reaction if conducted in different reaction systems. In general, the reaction time is in the range of from 0.05 seconds to 24 hours, preferably in the range of from 1 second to 12 hours.
Pressure of the reaction is generally not a critical parameter unless it is necessary to maintain a more desirable concentration(s) of the monomer(s) for the polymerization step or to facilitate flows in a continuous reactor. A suitable pressure is in the range of from 10 kPa to 2 MPa. A preferred pressure is in the range of from 50 kPa to 500 kPa. An inert or non-reactive atmosphere also may be used and is preferred. The selection of a particular inert or non-reactive gas may depend on the reactants used to ensure chemical compatibility and no change of critical reaction parameters such as pH. Suitable inert or non-reactive gases include, but are not necessarily limited to nitrogen, argon, carbon dioxide, methane and mixtures thereof. Nitrogen is a preferred inert gas. Air or diluted air also may be used provided that there is no interference with the chemical/physical stability of the components used or the desired polymerization reaction.
After the polymerization reaction is completed, the polymer products, ICPs, may be separated or recovered by a number of methods which are known to be suitable for emulsion polymers. Examples of such separation or recovery include, but are not necessarily limited to sedimentation, filtration, solvent removal, concentration, centrifugation, coagulation, spray drying, and combinations thereof.
The ICPs or other polymer products can be analyzed or characterized by a number of analytical tools to determine what type of polymerization has taken place, and what level of conductivity has been achieved. The specific chemistry or chemistries discussed herein are not intended to limit the scope of the present invention.
An ICP produced by the method of the present invention can be further doped with a dopant under proper reaction conditions. If desired, doping may be repeated several times with the same or a different dopant by the same or a different method. Suitable dopants are known to further increase the conductivity of an ICP. Examples of suitable dopants include, but are not necessarily limited to: HCl, BF3, PCl5, AlCl3, SnCl4, WCl6, MoCl5, Zn(NO3)2, tetracyanoethylene, p-toluenesulfonic acid, trifluoromethyl sulfonic acid and mixtures thereof.
In one method of doping an ICP, an undoped ICP is brought into contact with a dopant material as a solid, liquid, vapor, or solution. Examples of solvents suitable for making dopant solutions include, but are not necessarily limited to N-methylpyrrolidone, methanol, ethanol, tetrahydrofuran, acetonitrile, diethyl ether and mixtures thereof. Selection of a solvent depends on many factors, including the solubility of a particular dopant, chemical and/or physical compatibility between ICP and the solvent, chemical and/or physical compatibility between the dopant and the solvent and others. Preferably, a solution has a dopant concentration in the range of from about 0.05 Molar to about 2.5 Molar.
In another embodiment of the present invention, the ICP product, with or without a dopant also may be mixed, blended, admixed with one or more other materials to form a desired product. Such other materials include, but are not necessarily limited to carbonaceous materials, metal oxide powders and polar polymers materials and mixtures thereof. Examples of carbonaceous materials include, but are not necessarily limited to carbon black, graphite, amorphous carbon, activated carbon and mixtures thereof. Examples of metal oxide powders include, but are not necessarily limited to iron oxides. Examples of polar polymers include, but are not necessarily limited to polyesters, polyamides, and mixtures thereof. The amount of such other materials present is in the range of from about 1% to about 99% by weight based on the total weight of the final blend or mixture.
The present invention is further illustrated by the examples below. These examples are not intended to limit the scope of the present invention which is defined by the claims and the specification.
Using a mono-disperse polystyrene-co-4-vinyl pyridine, P(ST-4-VP=85/15) latex, we have established that by pre-emulsification of each of the aromatic monomers with a mixture of an emulsifier and xcex2-MCD, the monomer droplets are easily transported to the latex particles. Evidence of absorption of the monomer droplets by the latex particles was obtained by optical microscopy. We have found that the latex particles increase in size from an average of 80 nm to a maximum of 180 microns when brought into contact with the monodispersed emulsified monomer droplets. In the absence of xcex2-MCD, a mixture of cyclic heteroatom containing polymerizable monomer and an emulsifier produces a precipitate.
The graft copolymerization of the aromatic monomers within the latex particles is efficiently initiated at room temperature and thereafter continued at 0xc2x0 C. to yield a colloidal dispersion.
As discussed previously, the addition of methyl xcex2-cyclodextrin (xcex2-MCD) to the emulsified monomer mixture increases the compatibility of the aromatic monomers (aniline, pyrrole, furan and thiophene) in the aqueous phase by complexation. Because of the irregular size of the monomer droplets, the swelling of the latex particles in the absence of xcex2-MCD is nonuniform and exceeded the predicted maximum particle size for a given ratio of monomer to latex particle concentration. In the absence of the latex, a typical mixture that composed of monomer, emulsifier, water and xcex2-MCD, separates into distinct organic and aqueous phases upon standing undisturbed for a few minutes.
We have further discovered that the stability of the emulsified monomer mixture can be significantly improved by the addition of a minimum of 0.02 weight percent (based on the weight of aromatic monomer) of a poly(vinyl alcohol-co-vinyl acetate=88/12) (PVOH) copolymer. Optical microscopy of mixtures comprising of: surfactant, aniline, water, PVOH and an acrylic latex, reveals particles of uniform size comparable to the calculated average diameter for a monomer swollen latex particle of known average diameter.
We have also discovered that latices of 4-vinyl pyridine copolymers are stable in the presence of the required high concentration of the acidified redox pair, such as FeCl3/(NH4)2S2O8, used in catalyzing the polymerization of the aromatic monomers.
The acrylic precursor latices were prepared by emulsion polymerization of commercially available: methyl methacrylate (MMA), poly(ethylene glycol (200/400) monomethacrylate, butyl acrylate (BA), ethyl acrylate (EA), methacrylate (MA), methacrylic acid (MAA), styrene, N-vinyl pyrrolidone (NVP) and 4-vinyl pyridine (4-VP) monomers. A typical acrylic copolymer comprising of 15 weight percent of 4 VP and the remainder MMA was prepared by an emulsion polymerization technique as follows: A monomer mixture was prepared, having methyl methacrylate: 4-vinyl pyridine ratio of 85:15. The mixture contained 53.0% of MMA, 9.3% of 4 VP, 0.19% of N-dodecyl mercaptan, 36.7% DI (de-ionized) water and 0.8% of a 10% aqueous sodium dioctyl sulfosuccinate (SOLUSOL-75) solution(all by weight). Each monomer mixture was polymerized according to the following procedure. To an appropriate glass vessel equipped with stirrer, heater, a reflux condenser, and nitrogen sparge tube, was added 95.9% of deionized water, and 0.03% of sodium carbonate. The mixture was sparged for one hour with nitrogen while heating to 70xc2x0 C. The sparge rate was then changed to a sweep and 2.8% of a 10% aqueous solution of SOLUSOL-75 was added to the mixture. The temperature of the reaction vessel was then raised to 85xc2x0 C. At this temperature 124.96 ml of the initiator mixture that consisted of 0.35% of sodium persulfate and 99.65% of deionized water was added to the reaction vessel. The monomer mixture was then fed into the reaction vessel at the rate of 51.84 ml/min. As the polymerization proceeded, the initiator mixture was added to the reaction vessel at the rate of 124.96 ml every 15 minutes. The accumulation of solids was measured every 60 minutes just before the addition of the initiator mixture. At the completion of the initiator and monomer addition the mixture was held at 85xc2x0 C. for one hour.